The present invention generally relates to a detector chamber. More particularly, the present invention relates to a detector chamber for use in a smoke alarm.
Fires may start in many ways and may burn with differing characteristics. For example, a fire may be lit by a match, may flame quickly, and may constantly build in size. Alternatively, a fire may be started by overheating which may smolder for hours, if not days, to build up enough heat to ignite. In either scenario, the fire emits certain signature materials to a greater or lesser degree. Fire detectors are typically designed to sense one or more of these signature materials and sound an alarm if the signature materials are detected. Additionally, designing fire detectors to sense more than one of these signature materials may improve the ability of the fire detector to more rapidly detect fires.
More specifically, smoke, the byproduct of fire, is made up of many constituents and several of the constituents have signatures that may be sensed and used to detect the smoke and consequently the fire that produced the smoke. For example some fire detectors sense specific gases like carbon monoxide. Alternatively, some fire detectors sense the heat of the fire directly. Other fire detectors sense the particles that make up the smoke by analyzing the air flowing through the fire detector and detecting particles that are suspended in the air.
Specific types of fire detectors have advantages. For example, smoke detectors of the ionization type detect smaller particles as are found in greater abundance in flaming fires. Conversely, smoke detectors of the photoelectric optical type detect larger particles as are found in greater abundance in smoldering fires.
More particularly, photoelectric type smoke detectors typically respond to larger size particles (usually around 1.0 micron in diameter and larger) while ionization type smoke detectors respond to smaller particle sizes (usually around 1.0 micron in diameter or less). However, if an ionization detector were able to detect larger particle sizes as in smoldering type smoke or a photoelectric optical type smoke detector were able to detect smaller particle sizes as in flaming type smoke, the ability of a detector including these improvements to detect fires would be improved. This is especially important because users that are trying to protect themselves from a fire have no way of knowing how a detrimental fire may start. In order to provide this advantage, some smoke detectors combine ionization and photoelectric sensors in one smoke detector. However, such dual-mode fire detectors are quite costly.
In addition, a good smoke detector needs effective smoke entry, for example for any incipient fire with low heat to get the particles into the detection chamber.
Additionally, earlier photoelectric smoke detectors have experienced adverse effects due to the build-up of dust and dirt inside the detector. In some cases, the dust/dirt increases the background light, called noise, in the chamber which reduces the signal-to-noise ratio (SNR). Conversely, a higher SNR is more desirable because it allows particles to be more easily and reliably detected.
U.S. Pat. No. 6,876,305 to Kadwell teaches a compact particle sensor. As shown in FIG. 5, Kadwell teaches reflecting an emitted beam of light several times in the interior of a detecting chamber in order to provide a greater beam length to increase the chance that a particle will interact with a beam and be sensed by the detector. However, Kadwell suffers from the drawback that the light beam may interfere with itself where the light beams cross and that a single particle in the chamber may produce either no response if the particle does not intersect a beam or may produce a non-linear response if the particle intersects multiple beams, regions of differing beam intensity, or reflects a beam so that the beam interferes with another beam. Also the reflective surfaces may gather dust and get dirty and thereby significantly increase the noise in the chamber.
Similarly, U.S. Pat. No. 7,075,445 to Booth teaches a smoke detector having a greater effective light propagation path. As shown in FIG. 4, light is reflected in the interior of a chamber so that the light beam reflects from both walls several times in order to increase the propagation path. Booth suffers from the same drawbacks outlines above in Kadwell.
Thus, there is a long felt need for a fire/smoke detector that provides more rapid detection of all types of fires and increased reliability. Further, a single ionization detector or single photoelectric detector that may detect a wider range of particle sizes may enhance the ability of the detector to detect a fire more quickly and should be less costly than a dual ion/photo fire detector. Further, a detector that does not suffer from the drawbacks of Kadwell and Booth outlined above would be desirable.